Hearing loss occurs in approximately one in ten North Americans and in approximately one in ten of these persons, it is classified as profound.
Tinnitus or “ringing” noises in the ears are perceived by about 20% of the population in North America. Approximately 1 million persons in the U.S. alone are experiencing sufficiently severe tinnitus that it impairs their ability to cope with daily life.
Hearing aids for deaf persons have been getting smaller and their function has improved with advances in technology. Great changes have occurred over the years, advancing from the nineteenth century “ear trumpet” to small devices which fit in the ear canal and are not visible externally. A logical development is to implant the aid surgically.
A number of patents are relevant or of interest. Ball et al. in U.S. Pat. No. 5,800,336, describe a “floating mass transducer” with an electromagnet attached to one of the middle ear bones, the incus, such that it drives the ossicular chain. U.S. Pat. No. 5,558,618, Magnilia, describes a device consisting of a magnet mounted to the ossicular chain driven by an implanted electromagnetic coil. Dormer, in U.S. Pat. No. 6,277,148, describes a middle ear magnet driven by a coil placed in the external auditory canal, Leysieffer et al., in U.S. Pat. No. 5,772,575, describe another vibrating piezoelectric device for direct stimulation of the ossicles, Lenhardt et al., in U.S. Pat. No. 5,047,994, describe a device that takes external sound waves and transmits corresponding mechanical vibrations to the human skull.
Most surgically implantable hearing aids suffer among other things from the disadvantage that they involve altering or connection to the ossicles or small bones of the middle ear. These bones are very fragile with tenuous blood supply, and pressure on these ossicles from any direction leads to halisterisis or dissolving of the bone at the point of attachment. This phenomenon occurs either immediately or over a short period of time.
A second disadvantage of implantable hearing aids that connect to the ossicles is that the surgery is complicated and delicate, and admits the possibility of damage to the middle ear membranes, or to the ossicular blood supply or to adjacent structures such as the facial nerve.
A third disadvantage of implantable hearing aids that connect to the ossicles is that the production of vibratory forces via the ossicles or through the middle ear causes sound to exit the ear via the tympanic membrane. This frequently gives rise to auditory feedback or “squealing” which is familiar to users of in-the-ear hearing aids.
There exist other implantable hearing aids that do not involve connection to the ossicles and instead impart mechanical vibrations directly to the skull. Bone anchored hearing aids suffer from the disadvantage that they require insertion in and osseointegration with bone. Because of this, implantation of bone anchored hearing aids is difficult in pediatric patients whose skull bones are thin, soft, immature or malformed.
There is thus a strong need for a hearing aid device that does not damage the middle ear or ossicles; can be implanted surgically with minimum damage to the surrounding structures, for example the facial nerve; which, by design, does not cause auditory feedback; and which does not vibrate the skull by contact insertion.
Tinnitus maskers are devices that produce a sound external to the sufferer and distract the sufferer from hearing the internal noise that is currently believed to be in the brain itself. In this respect, this device could be affected electronically to produce a percept for masking tinnitus in human beings.
The use of an implantable aid with a cochlear implant is becoming more common as new cochlear implant surgical techniques frequently use gentle surgery that leaves existing hearing intact.